Democracy and the Prisoner's Dilemma
Democracy doesn't scale. It works fairly well for governing things like cities and towns, but on a scale like that of the United States' federal government it just doesn't work. The evidence of this is all around us, from low voter turnout to the stranglehold the two-party system has on the federal government, even as both sides converge more and more. This problem is a form of the free rider problem, caused by a kind of prisoner's dilemma.
In this case, I mean that even though being a good citizen might have benefits to society greater than the cost to each individual, those benefits are so diluted that from a pure self-interest perspective it isn't worthwhile to be a good citizen. For example, suppose it takes one hour of time per week to be a good citizen, and further suppose that if everyone spends this hour every week the result will be good government; while if no one does, the result will be bad government. Now look at the choices of "Bob," a typical citizen: Bob can either spend an hour on Saturday to go vote, or he can go bowling for an hour. Bob would be willing to spend the hour voting in exchange for getting good government, but he realizes that whether or not he votes, the overall result is the same: if everyone else votes, he'll get good government whether or not he votes, and if no one else votes he'll end up with bad government no matter what he does. So from a strictly self-interested point of view, Bob would choose to go bowling instead.
Of course, any given individual may have other reasons for voting, like a sense of civic or moral duty, but to rely on people's selflessness or sense of responsibility as the basis for a form of government is folly. Remember the reason capitalism works so well: people acting in their own self-interest end up providing a benefit to others, and to society.
This is also related to the problem of special-interest groups pushing their own projects through Congress despite that they may not be in the best interests of society as a whole. Take farm subsidies as an example: there is a small group of people (farmers) who receive a very concentrated benefit from such legislation, so they have a high incentive to lobby for it. On the other hand, the cost of the subsidy is spread out among a much larger group, so the cost to each other individual is low enough that it's simply not worth that individual's time and effort to combat the subsidy.
The founding fathers recognized this, which may be why many of them were so wary of a strong federal government. They left two basic means to combat the accumulation of power in the federal government: one of them was the familiar three-branch system, but the other was the states themselves. As the tenth amendment in the Bill of Rights states:
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Before the formation of the United States, and for quite some time afterward, the individual states were far more autonomous than they are now. Each state had a much more potent sense of identity: Thomas Jefferson is said to have considered himself a Virginian first, and a United States citizen second, for example. What this all means is that when the federal government tried to overstep its bounds, the states were expected to help put it back in its place. Unfortunately that safety measure has completely failed by now, and as a result the federal government is far larger than (in my opinion) any of the founders could have envisioned or desired, even the Federalists.
The expansion of the federal government also exacerbates the prisoner's dilemma: when a given power of government exists at the national level intead of in the cities and states, then any citizen who wants to change the way that power affects his own life must compete with an entire nation of other voters, instead of only a city or state's population. Were we to push more of the government's power down in the hierarchy (from the federal government down into the states), not only would an individual's vote have more effect on the role of government in his own life, but in addition a much greater diversity of governing styles could develop. That means it would be much more worthwhile to move to another state in case of dissatisfaction with one's own.
I wish I knew an easy way to accomplish this; for now, I think spreading the word as I'm doing is probably the best option. Go ahead and vote, too, but please vote for the candidate you like the best, not the one out of the two major parties that you hate the least. After all, if one's vote is ineffective in the first place, one need not worry about throwing it away by choosing a third-party candidate!